AstraZeneca says advanced trial shows its COVID-19 vaccine is 79% effective

London — AstraZeneca said Monday its COVID-19 vaccine provided strong protection against disease and complete protection against hospitalization and death across all age groups in a late-stage U.S. study. 

The British drug manufacturer also said its experts didn’t identify any safety concerns related to the vaccine, including any surrounding a rare blood clot that was identified in Europe. Scientists found no increased risk of clots among the more than 20,000 people who got at least one dose of the AstraZeneca shot.

AstraZeneca said the advanced trial data on the vaccine it developed along with Oxford University shows it is 79% effective.

Although the vaccine has been authorized in more than 50 countries, it hasn’t been given the green light in the U.S. yet — and has struggled to gain public trust amid a troubled rollout.

The U.S. study was made up of 30,000 volunteers, 20,000 of whom were given the vaccine while the rest got placebo shots. The results were announced Monday.

In a statement, AstraZeneca said its vaccine had a 79% efficacy rate at preventing symptomatic COVID and was 100% effective in stopping severe disease and hospitalization.

Investigators said the vaccine was effective across all ages, including older people – which previous studies in other countries had failed to establish.

It will take AstraZeneca and Oxford a few weeks to get the data ready to give the Food and Drug Administration to seek emergency approval for the vaccine’s use in the U.S., Oxford professor Sarah Gilbert told BBC radio, according to the Reuters news service.

The findings from the U.S. study are just one set of information they must submit to the agency.

An FDA advisory committee will publicly debate the evidence about the shots before the agency decides whether to allow the emergency use.

“These findings reconfirm previous results observed,” said Ann Falsey of the University of Rochester School of Medicine, who helped lead the trial. “It’s exciting to see similar efficacy results in people over 65 for the first time.”

Julian Tang, a virologist at the university of Leicester who was unconnected to the study, described it as “good news” for the AstraZeneca vaccine.

“The earlier U.K., Brazil, South Africa trials had a more variable and inconsistent design and it was thought that the U.S. FDA would never approve the use of the AZ vaccine on this basis, but now the U.S. clinical trial has confirmed the efficacy of this vaccine in their own clinical trials,” he said.

Human trials in the U.K. have also shown that the AstraZeneca vaccine likely helps prevent asymptomatic infection with COVID-19, which means it could help prevent the spread of the disease in addition to keeping people out of hospitals. 

Initial research released in early February was backed up with a peer-reviewed study showing the full two-dose regimen of the vaccine was about 50% effective at preventing any infection at all. “After the second dose, the two standard doses schedule had an efficacy of 49.5%. These data indicate that ChAdOx1 nCoV-19, used in the authorized schedules, might have a substantial effect on transmission by reducing the number of infected individuals in the population,” according to the study published in The Lancet.

Scientists have been awaiting results of the U.S. study in hopes it will clear up some of the confusion about just how well the shots really work.

Britain first authorized the vaccine based on partial results from testing in the United Kingdom, Brazil and South Africa that suggested the shots were about 70% effective. But those results were clouded by a manufacturing mistake that led some participants to get just a half dose in their first shot – an error the researchers didn’t immediately acknowledge.

Then came more questions, about how well the vaccine protected older adults and how long to wait before the second dose. Some European countries, including Germany, France and Belgium, initially withheld the shot from older adults and only reversed their decisions after new data suggested it is offering seniors protection.

Last week, more than a dozen countries, mostly in Europe, temporarily suspended their use of the AstraZeneca shot after reports it was linked to blood clots. On Thursday, the European Medicines Agency concluded after an investigation that the vaccine did not raise the overall risk of blood clots, but could not rule out that it was connected to two very rare types of clots.

France, Germany, Italy and other countries subsequently resumed their use of the shot on Friday, with senior politicians rolling up their sleeves to show the vaccine was safe.